Automatic dry coke weight system

ABSTRACT

An analog electrical system utilizes a signal from a coke weighing system and a signal from a coke moisture gauge to correct for prior errors in hopper weighings due to delivery overshoot as well as moisture variations in prior batches of coke.

United States Patent "1191 List et 'al. I

1111 3,814,914 June 4, 1974 AUTOMATIC DRY COKE WEIGHT SYSTEM Inventors:Harold A. List; Jack H. Baker, both of Bethlehem, Pa.

Bethlehem Steel Corporation, Bethlehem, Pa. 1

Filed: June 5, 1973 Appl. No.1 367,264

Assignee:

us. c1 235 1511, 177/50, 177/59. 177/120, 177/164, 214/18 R, 235/151.33,266/27 1m. (:1. 606g 7/66, G01 g 13/02, G01 g 13/28 Field ofSearch,177/50, 59, 70, 120, 164; 214/18 R; 235/151,151.13, 1511,1513;

References Cited UNITED STATES PATENTS 11/1969 Burn et a1. 177/503.502.162 3/1970 Munson 177/50 Primary Examiner-Malcolm A. MorrisonAssistant ExaminerR. Stephen Dildine Attorney, Agent, or Firm-Joseph .1OKeefe 5 7] ABSTRACT An analog electrical system utilizes a signal froma I coke'weighing system and a signal from a coke moisture gauge tocorrect for prior errors in hopper weighings due to delivery overshootas well as moisture variations in prior batches of coke.

2 Claims, 2 Drawing Figures AUTOMATIC DRY COKE wrzrcr-rr SYSTEM IBACKGROUND OFTHE INVENTION This invention relates to material handlingsystems, and more particularly to systems for periodically supplyingbatches of coke to a blast furnace.

In the operation of a blast furnace, a plurality of substances, viz.iron ore, fluxes and a source of carbon such as coke, is periodicallysupplied to the top of the furnace. Thecarbon in the coke reduces theiron ore and also provides the heatnecessary for the chemical reactionsin the furnace to take place. The main product of the furnace is iron;useful byproducts are slag and hot gases for heating in other processes.

' .ln order to insure that the iron ore is substantially completelyreduced, it is necessary to provide an excess of carbon to the furnace.However, too much of an excess results in wasted coke as wellas ironhaving an improper chemistry; in addition, hot gases too rich in carbonare produced, and the composition of the slag is improper. For thesereasons, it is desirable to closely control the amount of carbon in eachbatch of coke supplied to the furnace. Typically, a batch may consist ofthree weighings.

The coke which is supplied to the furnace, being naturally porous,contains moisture in varying amounts. Thus, weighing systems designed toprovide constant weight batches of coke must be provided with means tocompensate for the moisture in the coke. In addition, means must beprovided to compensate for the inevitable errors in weight which occurfrom weighing to weighing due to overshoot, i.e., the additional amountof coke supplied to the weigh hopper after the coke shut-off signal hasoccurred. t

In the past,-attempts have beenmade to correct for moisture by measuringthe moisture content of a sample of coke from a supply being fed to adelivery car, feeding this value to a computer, determining thecorrected coke weight, and using this value for controlling thetermination of supply to the car. However, no accurate means hasbeenavailable for determining the moisture content of coke in a shortenough period of time for this type of system to be satisfactory.

Attempts have been'made to compensate for variations in overshoot byaccumulating errors over a long period of time until a predeterminedvalue is reached, at which time a compensatory amount of coke issupplied to the furnace. However, this type of system does not solve theproblem of supplying a substantially correct amount of coke at eachbatch delivery, and this results in iron and byproducts of varyingchemistry, and requires more total coke to be sure that the amount ofcoke does not go below the minimum required to keep the furnaceoperating.

It is an object ofthis invention to provide a system for supplying foreach weighing of material a control signal which rapidly corrects forall moisture-based and weighing-based errors in priorweighingsofmaterial.

SUMMARY OF THE INVENTION signal indicative of the moisture content ofthis weighing, and further means is provided for producing a thirdsignal indicative of the target dry weight for this quantity ofmaterial. Means is provided adapted to receive said first, second andthird signals and compute and store a fourth signal indicative of thetarget dry weight plus (a) the difference-between the target dry weightand the actual dry weight of the instant weighing, and (b) the error indry weight existing after the next preceding weighing. Further means isprovided to receive the second signal and the fourth signal and computeand store a fifth signal indicative of the actual desired weight for thenext weighing. This assumes that the moisture content of the nextweighing will be the same as the moisture content of the instantweighing. Timing means is provided for controlling when these fourth andfifth signals are computed and stored. .Means is provided for shuttingoff the supply of material for the next weighing when the first signalequals the fifth signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of thecircuit of the invention.

FIG. 2 is a schematic diagram showing the sequence of events duringstart-up and the initial weighing cycle,

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, the subjectcircuit comprises a voltage follower 10, connected to a potentiometer 12attached to the balance which indicates the actual weight of thematerial in a hopper (not shown) which is to empty into a delivery carperiodically supplying coke to a blast furnace. The output of thevoltage fol-1 lower 10 is a first signal E, indicative of the totalactual weight of the coke, i.e., the dry coke plus moisture, in thehopper.

The output of the voltage follower I0 is supplied to a comparator 14which operates a control relay 16 to stop a conveyor belt supplying coketo the hopper. The comparator l4 actuates the relay 16 when the signalfrom the voltage follower l0 equals the set point of the comparator, thedetermination of which will be hereinafter explained.

After the supply of coke to the hopper has terminated, the moisturecontent of said coke is determined by moisture-measuring means 18, e.g.a nuclear gauge. This gauge comprises a source of gamma radiation whichmeasures the mass or bulk density of the coke, this value varying withthe size of the coke particles. That is, a charge of coarse coke willnot be as dense as a charge of fine coke. The gauge also provides asource of fast neutron radiation which measures the hydrogen density ofthe coke. From these measurements, the gauge automatically computes thepercentage moisture in the coke. Other types of moisture measurementgauges which give a fast response could also be used. Means 18 producesa signal, herein referred to as the second signal E indicative of thepercentage moisture of the coke in the hopper. After the moisturecontent is determined, the hopper is emptied into the delivery Theoutput from the multiplier-subtractor 20 is fed through a switch 22,normally closed at all times except during initial start-up, to'anadder-subtractor 24. Also supplied to the adder-subtractor 24 is asignal, herein referred to the third signal E;,, from a reference module26. This signal is indicative of the target dry coke weight required forproper blast furnace operation. The adder-subtractor 24 subtracts theactual dry weight of the instan t'weighing, indicated by the output fromthe multiplier-subtraetor 20, from the target dry coke weight to obtainthe error'in weight on the instant weighing.

The output from the adder-subtractor '24 is fed to a sample-and-holdmodule 28, the output of which is fed through a second sample-and-holdmodule 30 through a switch 32, also normally closed at all times exceptduring initial start-up, back to the adder-subtractor 24.

As will be explained later, the output from the sampleand-hold module"30 represents the target dry coke w'eight'plus the error in dry cokeweight existing after the previous weighing. Thus, the output of theaddersubtractor 24 is seen to represent the sum of: (l) the net errorexisting after all previous weighings; (2) the error in the instantweighing; and (3) the target dry coke weight. This signal is hereinreferred to as the fourth signal E and represents the total dry cokedesired in the next weighing to eliminate all previous errors.

The fourth signal is fed to a divider-subtractor 34 where it and .thepercentage moisture signal from means 18 are combined to produce asignal, herein referred to as the fifth signal E representative of theactual weight of the next weighing of coke necessary to eliminate anyprevious errors, assuming that the moisture of the coke in the-nexthopper to be weighed is the same as that of the coke just emptied intothe delivery car. This fifth signal is supplied to a sample-and-holdmodule 36 where it functions as the set point signal for the comparator14.

The operation of the subject invention will now be described utilizingFIG. 2 and TABLE I in conjunction with a specific example in which thetarget dryeoke weight ,is 4,000 pounds.

Initially, i.e. at time t a moisture content must be assumed since thereis no coke in the hopper. Thus, switch 22 is opened and, since there isno previous error. switch 32 is also opened. For the example shown inTABLE I, an initial moisture content of 0% is assumed.

initially, all of the sample-and hold modules 28, 30 and 34 are in thesample mode. The signal from the refqr medals ituiz- 0 i is t ed th uadder-subtraetor 24 an sample-and-hold 28 to dividersubtractor 34,where, since the input from moisturemeasuring means 18 is zero, theoutput to sample-andhold 36, and hence the setpoint fed to comparator14, is 1 9 4999.1 ,mit hes. 2. n a e h n ed a time t,.

Again referring to F IG. 2, at time 1 the hopper begins filling and attime t the filling of the hopper is terminated when the signal from thevoltage follower 10 equals the setpoint from the sample-and-hold module36. However. due to a natural overshoot of the coke handling systemwhich, for the purpose of the example is assumed to be 300 /weighing, atotal actual weight of 4300 of coke is in the hopper. This weight signalis supplied to the multiplier-subtraetor from time 1;,

r to time t after which time interval the hopper is autoin thehopper..This measurement is complete by time 1 and a signal representingmoisture is fed to the multiplier-subtractor 20 and thedivider-subtractor 34 during the interval t -I In the present example,it is assumed that the moisture content of the first weighing wasmeasured as 5%.

At time i the system is automatically switched into the compute mode.Sample-and-hold modules 24 and 36 switch into the sample mode, whilesample-and-hold module 30 switches into the hold mode, holding thesignal previously in module 28, viz. the target dry weight 0f 00Q Theoutput from the multiplier-subtractor 20 represents the dry coke Wightin the hopper, viz. of 4300 i.e. 4085 The adder-subtractor 24 thusreceives the following three inputs: (a) 4000 from the sample-and-holdmodule 30; (b) 4000 from the reference module 26; and (c) 4085 from themultipliersubtraetor ZOITh e adder-substractor 24 adds (a) to [(b)e)] toget a desired dry coke value of 3915 It is noted that (a) represents thetarget dry coke weight plus any errors accumulated during all previousweighings, while [(b)(c)] represents the dry coke weight error of theinstant weighing.

The desired dry coke value for the second weighing, i.e. 3915 is fedthrough sample and-hold module 28 which is in the sample niode, to thedivider-subtraetor 34 where it is combined to obtain the desired grossweight of the next weighing, i.e. the set-poinL'This, of course, assumesthat the moisture content of the next weighing is the same as that ofthe instant weighing. The output of thedividersubtraetor 34, which is4121 is fed through the sample-and-hold module 36, which is in thesample mode, to the comparator 14.

The calculation period automatically ends at 1 and sample-and-holdmodule 36 switches into the hold mode, holding the proper setpoint valuefor the next weighing. At the same time, sample-and-hold module 28switches into the hold mode, holding its value for the nextcalculations, while sample-and-hold module 30 switches into the samplemode so it can receive the signal from sample-and-hold module 28 duringthe next calculation.

At time the weight signal from the voltage follower 10 is terminated andthe hopper begins emptying. The hopper is substantially completely emptyby time I the moisture signal from means 18 is terminated, and thehopper begins to automatically refill. The cycle then repeats itself.

The timing of the filling and emptying of the hopper is controlled bythe charging control system of the blast furnace, this system beingconventional. The moisturemeasuring means 18 automatically provides asignal when the level of the coke exceeds the point in the hopper atwhich the measurement is taken. A reliable signal, however, is notavailable until a short time after the hopper is filled, eg at 1,,because of the time delay of the moisture-measuring means.

A standard cam-timer automatically starts when the hopper begins tofill, and initiates and terminates the compute cycle at and 1respectively.

The setpoint for the second weighing, as above adder-subtractor 24 is3915 the value previously stored in module 28, plus 4000 (from referencemodule 26), minus the dry coke weight in hopper, viz. 20 .h QAFRQPQ? hdd -su reqqrw i 3715 4, which is fed to the divider-subtractor 34 whereit is divided by 95% to determine the setpoint for the third Table 1 shows the values at various points in the subject circuit carried throughthe first l weighings.

The values are expressed in percentage moistureand pounds rather thanvoltages. For illustrative purposes,

the moisture is shown as varying inmuch larger increme'nts than wouldnormally occur; generally, the moisture varies by no more than 2 or 3%from weighing to weighing. Column 9 shows the error for batches of cokeconsisting of three weighings. This figure is important, since the blastfurnace operates essentially as a batch process, and in the case of theblast furnace to which the subject invention was applied, each batchincluded three weighings of coke. As can be seen, the actual amount ofdry coke delivered per batch varied from the desired amount. viz. 12,000pounds, by a max imum of only 148 pounds for the examples shown. It isnoted that this error is nearly balanced by the error in 6moisture-containing material, comprising:

a. means for producing a first signal indicative of the actual weight ofeach discrete quantity of material; b. means for producing a secondsignal indicative of 5 the moisture content of said material; 4

c. means for producing a third signal indicative of the target dryweight for each weighing of said material; v d. means adapted to receivesaid first,-second an third signals and compute-and store a fourthsignal indicative of the target dry weight, plus the difference betweensaid target dry weight and the actual dry weight of the instantweighing, plus the error in dry weight existing after the next precedingweighmg;

e. means adapted to receive said second signal and said fourth signaland compute and store a fifth signal indicative of the actual desiredweight for the next weighing;

f. timing means for controlling when said fourth and fifth signalsare'computed and stored; and

g. means for shutting off the supply of said material to said nextweighing when said first signal equals said fifth signal.

2. Apparatus as recited in claim 1, in which means (d) comprises:

i. means for converting said first signal into an adjusted signalindicative of the actual dry weight of the instant weighing;

ii. means for summing said third signal, said adjusted signal, and asignal indicative of the error in dry weight exist in g after the nextpreceding weighing;

0 iii. means adapted to sample the signal from means (ii) during acompute period and to store said sigt h e nextjzatch, M u 5 nal duringall other periods; and

Gross Target wt. Instant plus (wet) Percent Dry wt. Target error errorShut off Batch Weigh cycle E1 HzOEz -2 E3 Ei-z-Ea E4 point E5 errorPreset 4, 000 4, 000 4, 000 1... 4, 300 5 4, 085 4, 000 3, 915 4,121

We claim: 1. Apparatus for automatically measuring and controlling thenet dry weight of discrete quantities of iv. means adapted to store theoutput of means (iii) during said compute period and to sample saidoutput during all other periods.

1. Apparatus for automatically measuring and controlling the net dryweight of discrete quantities of moisture-containing material,comprising: a. means for producing a first signal indicative of theactual weight of each discrete quantity of material; b. means forproducing a second signal indicative of the moisture content of saidmaterial; c. means for producing a third signal indicative of the targetdry weight for each weighing of said material; d. means adapted toreceive said first, second and third signals and compute and store afourth signal indicative of the target dry weight, plus the differencebetween said target dry weight and the actual dry weight of the instantweighing, plus the error in dry weight existing after the next precedingweighing; e. means adapted to receive said second signal and said fourthsignal and compute and store a fifth signal indicative of the actualdesired weight for the next weighing; f. timing means for controllingwhen said fourth and fifth signals are computed and stored; and g. meansfor shutting off the supply of said material to said next weighing whensaid first signal equals said fifth signal.
 2. Apparatus as recited inclaim 1, in which means (d) comprises: i. means for converting saidfirst signal into an adjusted signal indicative of the actual dry weightof the instant weighing; ii. means for summing said third signal, saidadjusted signal, and a signal indicative of the error in dry weightexisting after the next preceding weighing; iii. means adapted to samplethe signal from means (ii) during a compute period and to store saidsignal during all other periods; and iv. means adapted to store theoutput of means (iii) during said compute period and to sample saidoutput during all other periods.